I have been going over my mare's pedigree and all I can find are grays, chestnuts, and a handful of bays in there. I am curious as to where on earth my little black mare popped out of! If anyone could take run through it and let me know their theory on the little odd ball, I would greatly appreciate it!

Here it is, let me know how she came to be the color she is if you can with so little info.

Some of the colors aren't listed, but its very easy to get a black out of a bay. A bay is a black horse with a 'modifier' gene--the agouti gene--which tells the body to put the black only on the legs and mane/tail. If the horse doesn't pass the agouti gene and passes the black gene... your horse will be black, since black is pretty much dominant over most other colors (except maybe gray? Someone correct me if I'm wrong).

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I'm pretty sure that you're right At least that was how it was described to me. One of her parents was probably Heterozygous for the Agouti gene and passed on the recessive copy so the black was not passed on to your mare. That's how it usually works with mosts genes.

You are mostly correct-- except BOTH her parents would have to be heterozygous for agouti AND at least heterozygous for black as well. Both parents had to give her a non-agouti gene making her homozygous for non-agouti (aa) as well as as at least one parent giving her a black gene (E) making her at least heterozygous for black. Agouti and black are not either-or-- a horse who has black (E-) can also have Agouti (A-) -- meaning it would be a bay horse.

If either of her parents had been homozygous for Agouti, they would have passed one to her and she would be bay rather than black. (Chestnuts also have the pair of genes that are either homozygous Agouti (AA) homozygous for non-Agouti (aa) or heterozygous Agouti (Aa) but you can't tell by looking, because Agouti only acts on black and chestnuts do not have black pigment to be acted on, by virtue of being homozygous recessive for black (ee)).

Black (E) is dominant over non black (e) (AKA chestnut), And Agouti (A) is dominant over non agouti (a). That is why, even thuogh black is dominant, you do not see so many black horses-- the Agouti gene is very common in most breeds, and it makes a foal that is otherwise genetically black into a bay.

Also, grey is not a color in and of itself-- all horses are born with a genetic base color such as black, chestnut, or bay. When other "modifier" genes like the greying gene are inherited, they do not cancel out base color-- they simply act on that base color.

The grey gene causes a horse's colored hairs to gradually be replaced with white hairs as they age. So anywhere you see a grey in your horse's pedigree, realize that horse was genetically a bay, black, or chestnut before it turned grey-- but its registry simply called it grey so you don't know what its base color is unless you can find someone who saw it as a baby, or if the horse was gentically color tested, has enough various colored progeny to prove what it packs genetically, etc.

WOW! Thanks everyone! Haha, I'll have to work on my punnet squares to get a good feel for this again, haven't done it since freshman year in high school! That's interesting about the grey, I knew that they faded, but I didn't know that the gray isn't a "technical" color and that it would still pass on the chestnut, bay or whatever too! Neat, I love this stuff! I think I'll do more research on this, but I'm off to a big start thanks to you guys, especially East! How'd you learn all of this stuff?

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